Diseases of the cornea may be the leading cause of blindness worldwide. One of the most difficult to treat is caused by herpes simplex virus. Herpes keratitis accounts for more visual morbidity, medical expense, and loss of productivity among otherwise healthy individuals than any other corneal infection in Western countries. Fifty percent of persons developing herpes keratitis are likely to experience recurrence of epithelial disease or a complication of stromal keratitis within five years. Contemporary theory concerning the natural history of herpes virus infection is summarized by the neuronal hypothesis which assumes that as a result primary herpetic infection virus invades superficial nerve endings and is transported intraaxonally to corresponding ganglia where latency is established. Upon reactivation, virus or virus specified products are transported centrifugally in axons to target organs where they are released with or without the production of characteristic herpetic lesions. How and why latency is established and the mechanism(s) of reversal to active disease are currently unknown. There is no method for blocking establishment of latency or recurrence of disease. The fundamental problem resides in the definition of latency at the molecular level in human disease. The specific intent of this project is to characterize the state of the HSV-1 genome during latent and reactivating infection using molecular, antigenic and morphological parameters. Radiolabeled virus will be used as a probe with techniques of autoradiography and in situ hybridization to locate and quantitate viral DNA and to determine whether virus is being transcribed during latency. Radiolabeled HSV-1 DNA isolated from latently infected neurons will be studied to determine its relationship to host cell DNA and infectivity potential. Monoclonal antisera will be utilized to study viral inclusion bodies and the sequence of viral antigenic expression during the process of reactivation at the light and EM level. To increase efficiency and for simplification and potential amplification of some of the methodology, an in vitro model will be used in conjunction with the in vivo rabbit eye model. Elucidation of these molecular parameters may allow for therapeutic intervention to prevent recurrent disease.